1. Field of the Invention
The present invention generally relates to image processors for performing spatial and temporal alignment of two or more topologically similar rasterized images and, more particularly, to image processors of the type for use in subsequent processes such as the inspection system defect detection system described in application Ser. No. 07/806,942.
2. Statement of the Problem
Image processing as practiced in the area of printed circuit board inspection generally operates upon images generated as a raster of picture elements (pixels) by devices such as laser scanners, vidicons and linear charge-coupled device (CCD) arrays. Those pixels are converted from an analog form to a binary form for further processing. That processing is upon small sections of large fields of image data because it is more economical to operate on the directly acquired data than it is to store it for use by another method of processing.
3. Description of the Prior Art
While the translation and rotation of the real image might be corrected by mechanically rotating and translating the real object prior to the raster scanning acquisition of data, mechanical translation and rotation adjustments are of limited value when the mechanical precision is gross in comparison to the raster pixel resolution. As the image resolution is increased, mechanical precision must also be improved. When raster pixel resolution is measured in microinches, mechanical tolerances must be the same. A hostile environment (e.g., vacuum, temperature, inaccessibility, and vibration) may also preclude mechanical solutions. Magnification, minification, and distortion of the real image 20 may be produced by the raster scanning device 14' or by the original manufacture of the real object being imaged. These differences from the ideal are not amenable to compensation by mechanical or optical adjustments.
The prior art shows that parallel image processing is structured to operate identically on points in the image that are widely separated in the horizontal or vertical directions. No scheme exists in the prior art to process images in parallel by operating on their adjacent rasters.